Someone gave me a folding bike with 14" wheels, a "Roll n Fold" (cheap department store folding bike.) I was finding the gearing way too low for the wheel size (something like 32x18), so I swapped the rear wheel for a 16x1.75" coaster brake wheel from a kid's bike that uses the same type of cogs as a 3-speed. The new configuration is 42x13 which gives 3.5 meters development or 43.5 gear inches. (I also switched the front to a 16" wheel too by using forks from a kids' suspension MTB.) I may swap the 42t for something bigger at some point too. As it is now it's much more fun to ride than with the stock setup.
What I would like to do is build a rear wheel the same size around something like an Automatix 2-speed. I'm figuring the extra overdrive gear would give 4.7m or 59.2 gear inches. The thing is, I'm not coming up with much in my online searches for 16" rims with 36 spoke holes and I don't know a lot about selecting rims generally. I weigh 160 lbs and I'm basically looking for something fairly inexpensive that's strong enough to make a durable wheel. I'm thinking that with so many spokes on such a small wheel the rim may not need to be anything too fancy, but as I say I don't really know a lot about this stuff. I have done some reading on wheelbuilding but haven't done it.